Soluble Fiber Takes the Spotlight

Soluble fiber is a rising star in the ingredient world, in tandem with its fraternal twin, insoluble fiber. While the two are often linked, they do have significant differences once they find their way to the digestive system. Regardless, the term fiber on a label has powerful connotations.

According to AC Nielsens Label Trends report, products featuring fiber on the label grew by 10% or more for the 52 weeks ending Dec. 3, 2005, vs. the year before. Consumers have heard the message loud and clear about fibers health status, thanks to a number of leading organizations that have been singing its praise, including the American Heart Association (AHA), Dallas; American Diabetes Association, Alexandria, VA; National Cancer Institute, Washington, D.C.; and USDA, whose Dietary Guidelines for Americans, 2005, call for an increase in fiber intake. For decades, dietary fiber has been studied for its beneficial effects on cardiovascular disease (CVD), coronary heart disease (CHD), stroke, sudden death, hyperlipidemia, hypercholesterolemia, diabetes, obesity, the lower digestive tract and cancer. The National Academies Institute of Medicine recommends a dietary fiber intake for adults 50 years and younger of 38 grams for men and 25 grams for women, and for men and women over 50, at 30 and 21 grams, respectively. This poses a challenge, however, since Americans eat only about 15 grams of fiber per day.

Sorting it out 

Dietary fiberplant carbohydrates the body cannot digestis classified as either soluble or insoluble. Both serve important, but different, functions. Insoluble fibers are more closely associated with beneficial digestive effects, but soluble fiber brings additional benefits, such as heart health. With passive water-attracting properties, insoluble fiber helps to increase bulk, soften stools and shorten transit time through the intestinal tract. In contrast, soluble fiber is resistant to digestion and absorption in the small intestine, with complete or partial fermentation in the large intestine. Fermentation occurs by the action of colonic bacteria on the food mass, producing shortchain fatty acids. Its these short- chain fatty acidsbutyrate, propinate and acetatethat have such significant health properties, says Cristina Munteanu, food applications specialist, GTC Nutrition, Golden, CO.

Good sources of soluble fiber include legumes, oats, rye, rice bran, chia, barley, fruits (citrus, strawberries and apples), root vegetables and psyllium seed husk. Beta-glucan, the soluble fiber associated with oats and barley, is also found in yeast, bacteria, algae and mushrooms. Examples of soluble fiber used in functional foods and supplements include inulin, fructans, xanthan gum, cellulose, guar gum, fructooligosaccharides (FOS), and oligo- and polysaccharides. FDAs current recommendation for soluble fiber intake is 25% of total dietary fiber, approximately 6 grams per day.

To your health 

The major health benefits of traditional soluble fiber include blood glucose control, decreased lipid levels and regularity, says Munteanu, who adds that, more recently, the industry and consumers are buzzing about the health benefits of prebiotic fibers, as well.

Researchers increasingly suspect that a deficiency in total dietary fiber in the Western diet may be contributing to the current epidemics of diabetes, coronary artery disease and colon cancer. Studies indicate high total fiber intake might offer protection against metabolic syndrome, a cluster of factors that increases the chance of heart disease and diabetes. Both insoluble and soluble fiber appear to be protective against high C-reactive protein levels, a marker of acute inflammation and predictor of CVD and diabetes.

Soluble fiber stands out primarily due to its ability to lower lowdensity lipoprotein (LDL) cholesterol. According to AHA, regularly eating soluble fiber as part of a diet low in saturated fat, trans fat and cholesterol might decrease CVD risk because of a modest reduction in LDL cholesterol. Eating 5 to 10 grams per day of viscous soluble fiber reduces CVD risk by reducing LDL cholesterol blood leve1s 10% to 15%, with reduction in CVD events by 10% to 15%, according to the Department of Family Medicine and Community Health at the University of Minnesota, Minneapolis. Soluble fibers cholesterol-lowering ability is credited to changes in cholesterol or bile acid absorption, hepatic production of lipoproteins and clearance of lipoproteins.

Growing evidence indicates soluble fiber may help in glucose control, too. Postprandial blunting of blood glucose and insulin responses to carbohydrates can occur by supplementing soluble fiber in the diet. In a study published in the March 2007 issue of Asia Pacific Journal of Clinical Nutrition, highdose barley beta-glucan supplements improved glucose control when added to a high carbohydrate starchy food. And products prepared with barley flour enriched with beta-glucan showed favorable responses on glucose metabolism and insulinemic responses in a study published in the Journal of the American College of Nutrition (2006, 25:313-320).

Soluble fiber may even play a role in fighting obesity. Preliminary evidence suggests glucomannan, a highly viscous, fermentable soluble fiber, generally derived from Amorphophallus konjac, may promote weight loss due to its effects of promoting satiety and fecal energy loss. In a study published in the American Journal of Therapeutics (2007, 14(2):203- 212), researchers found that 6 grams of oat beta-glucan added to the AHA Step II diet, along with moderate physical activity, not only improved lipid profile, but decreased weight and reduced risk of cardiovascular events in overweight males with mild to moderate hypercholesterolemia.

Soluble fiber may also share intestinal health benefits with insoluble fiber. Soluble-fiber supplementation with glucomannan has been indicated for diverticulosis symptoms and acute diverticulitis. Soluble, nongelling fibers, like partially hydrolyzed guar gum, might address irritable bowel syndrome (IBS), as they can reduce constipation and diarrhea, decrease abdominal pain, contain prebiotic properties, and increase quality of life in IBS patients.

Some soluble-fiber benefits may come through its synergistic effects with other nutrients in a food. According to a study from the USDA Beltsville Human Nutrition Research Center, Beltsville, MD, published in the Journal of the American Dietetic Association (2006, 106(9):1380-1388), increasing whole grain foods, whether high in soluble or insoluble fiber, can reduce blood pressure and help control weight. Habitual wholegrain consumption was related to a 20% reduction in CHD and 40% reduction in CVD risk, but researchers reported that these benefits may be due to a synergistic effect of soluble fiber, insoluble fiber, magnesium, folate, and vitamins B6 and E.

Finding its way into foods 

The use of soluble fibers in the United States has grown, because they are frequently included in nutrition and cereal bars, yogurts, dairy products and nutritional beverages. Oats first basked in the glow of soluble fibers health halo when, in 1997, FDA allowed a health claim for beta-glucan soluble fiber found in whole oat foods and the reduction in risk of heart disease. Oats contain a significant amount of beta-glucan. According to Robert Serrano, vice president, product development, Grain Millers, Inc., Eugene, OR: While typical ranges in normal commerce are between 3.0% to 6.8%, we are starting to see new hybrids in the 7.0% to 7.5% range. But oats didnt hold reign over the soluble-fiber kingdom for long. Barleys beta-glucan gained a health claim for CHD risk reduction. In barley, we see a typical range from 4.5% to 6.0%, and hulless varieties from 5.0% to 7.5%, he says.

New ingredients followed, such as Oatrim, the soluble fraction of alpha-amylase hydrolyzed oat bran or whole oat flour, and soluble fiber found in psyllium seed husk. An oat-bran concentrate, OatVantage, from GTC Nutrition, is standardized to supply 17 times more betaglucan than common oats.

Any oat- and/or barley-containing product, particularly those formulated with oat bran and/or barley and/or high beta-glucan concentrates and/or isolates, can be formulated to meet the recommended 0.75 gram per serving, says Serrano.

Less familiar sources of soluble fiber are cropping up, each with its own unique properties and characteristics. A few include: guar gum, a viscous soluble dietary fiber and edible thickening agent; soluble fibers isolated from the seeds of Cassia tora Linn; and konjac glucomannan, a water-soluble fiber derived from the konjac root. In addition, an odorless galactomannan extract derived from fenugreek seeds produced by Frutarom, North Bergen, NJ, Fenu- Life, is suitable for dietary supplements, nutrition bars and powdered beverages.

The definition of dietary fiber developed by the AACC Dietary Fiber Definition Committee and adopted in 2000 also widens the range of soluble-fiber ingredients available. It reads: Dietary fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin, and associated plants substances. Dietary fibers promote beneficial physiological effects including laxation, and/or blood cholesterol attenuation, and/ or blood glucose attenuation.

One such ingredient, polydextrose, marketed by Danisco Sweeteners, Elmsford, NY, as Litesse, is a complex carbohydrate mainly composed of randomly cross-linked glucose. It resists digestive enzymes and provides prebiotic function to intestinal microflora. This 1 kcal-per-gram bulking agent shows physiological effects that allow it to be classified as fiber and can function as a fat replacer.

Other new ingredients include: Nutriose soluble fiber, a fermentable- resistant dextrin developed by Roquette, Lestrem, France, highlighted for beverage applications; Fibersol 2, from ADM, Decatur, IL, a 90%-fiber digestion- resistant maltodextrin from corn that does not hold water and works well in baked goods; and NutraFlora, developed by GTC Nutrition, a short-chain FOS for yogurt and smoothie products.

As the health benefits for soluble fiber continue to grow and gel in consumers consciousness, it appears the popularity of soluble- fiber-rich food products will have no where to go but up. 

Sharon Palmer is a registered dietitian with 16 years of experience in health-care and foodservice management. She writes on food and nutrition for newspapers, magazines, websites and books. Palmer makes her home in Southern California and can be reached at [email protected].